The present invention relates to a color copier, color printer, color facsimile apparatus or similar multicolor image forming apparatus and, more particularly, to a rotary developing device included in such an image forming apparatus.
Generally, a rotary developing device has a developing unit or revolver accommodating a plurality of developing sections therein. The developing sections are arranged around a rotary shaft on which the revolver is mounted. The revolver is rotated to bring one of the developing sections to a developing position facing an image carrier which carries an electrostatic latent image thereon. The developing section arrived at the developing position develops the latent image with a developer carrier on which a developer is deposited. This type of developing devices are disclosed in, for example, Japanese Patent Laid-Open Publication Nos. 63-78169 through 63-78175, 63-177165, 63-178262, 63-178263, 3-68973, 3-68970, 3-111868, 3-264967, 4-78873, 4-78875, 4-348368, 4-8790, 61-243467, 4-78872, 4-78884, 4-78876, 57-111555, and 64-40957 as well as in Japanese Patent Publication Nos. 64-8330 and 4-10071 and U.S. Pat. No. 5,168,319.
To produce an image of desirable quality with the rotary developing device, the developer carrier brought to the developing station must be accurately positioned relative to the surface of the image carrier. Also, a predetermined gap for development must be formed between the image carrier and the developer carrier. Further, vibration must be suppressed when the revolver is driven. The conventional developing devices taught in the above-mentioned documents cannot meet such requirements and, moreover, increase the cost due to complicated constructions.
Japanese Laid-Open Publication Nos. 57-111555 and 64-40957 mentioned above propose arrangements for applying a bias voltage to the developer carrier implemented as a roller. However, such arrangements are also extremely complicated.